Abstract: Chemical modifications of small molecule metabolites occur in every organism and play a fundamental role in essentially all biological processes, from the construction of the building blocks for genetic information storage and cellular enzymatic machinery to the continual processing of nutrients that sustains life. Although these reactions have been thoroughly investigated from an observational standpoint, there have been relatively few attempts to manipulate biological chemistry using tools and approaches from organic synthesis. This proposal details a strategy for developing biocompatible reactions, non-enzymatic chemical transformations that can be used to manipulate the structures of small molecules in the presence of living organisms. We have initiated preliminary investigations aimed at establishing a proof-of-concept for two approaches that connect biological and synthetic chemistry: the use of microbial metabolites as chemical reagents and the ability of small molecules to catalyze reactions that can support the growth of auxotrophic microorganisms. These experiments are designed to demonstrate that non-enzymatic reactions can proceed in the presence of microbes and have the ability to interact with microbial metabolism. The knowledge gained from these initial studies will then be applied to problems in the areas of synthetic chemistry, synthetic biology/metabolic engineering, and medicine. The challenges associated with this project are substantial; however, its potential scientific impact on multiple fields is significant. If successul, our ability to manipulate small molecules in vivo using chemical methods will open entirely new avenues for investigation at the interface of chemistry and biology with the potential to greatly impact human health. Public Health Relevance: The ability to chemically modify small molecules in living organisms has the potential for broad impact on multiple research areas related to public health, including synthetic biology and drug discovery. Biocompatible transformations, synthetic reactions capable of interfacing with the chemistry of life, will open up new methods for sustainably discovering and supplying important medications. In addition, the agents behind these transformations may themselves be used as therapeutics, and this novel mode of action would represent an entirely new way to think about designing small molecule drugs.